The present invention relates to a workpiece guide rail for a sewing machine, and more particularly to a guide rail which includes a sewing material stretching device for spreading out the material of the workpiece along the course of a seam prior to sewing.
In a known workpiece guide rail, disclosed in Federal Republic of Germany Pat. No. 20 22 735, the base of the guide rail is divided into short sections, each with spring action. Narrow leaf springs arranged alongside of each other are provided on its bottom, as a result of which the bottom of the workpiece guide rail can adapt itself to an accumulation of material in the region of the seam and also can cover locations directly adjacent the accumulation of material. This known workpiece guide rail, however, does not make it possible for the workpiece to be stretched in the region of the intended course of the seam prior to the sewing.
Accordingly, an important object of the present invention is to provide a guide rail with which it is possible, before sewing, to automatically elongate the workpiece which is to be sewn to a predetermined extent.
To carry out this and other objects, the invention includes a workpiece guide rail for a sewing machine for guiding a workpiece past a stitch formation point to determine the course of a seam, comprising a frame and a plurality of holding elements movably mounted on the bottom of the frame. Each holding element has a bottom surface adapted for gripping the workpiece. Means are provided for temporarily increasing a spacing between the holding elements by a predetermined amount in order to stretch the workpiece, and decreasing the spacing between the holding elements to their previous spacing in order to allow the workpiece to return to its previous dimensions. According to another aspect, the invention comprises means for interlinking the holding elements, and means for retaining each holding element movably mounted on the frame.
With the guide rail of the invention it is possible to sew multi-layer workpieces smoothly and free of wrinkles, by stretching the workpiece and thereby ensuring that for each stitch there is used a controlled amount of thread. Thus, a taut, wrinkle-free seam remains after sewing, when the workpiece has again resumed its original length.